1. Field of the Invention
The present invention relates to a piezoelectric resonator and an electronic component including such a piezoelectric resonator, and more particularly to a piezoelectric resonator including a piezoelectric resonator element vibrating in a longitudinal vibration mode, and an electronic component, such as an oscillator, a discriminator, and a filter, including such a piezoelectric resonator.
2. Description of Related Art
FIG. 34 is a perspective view showing an example of a conventional piezoelectric resonator. The piezoelectric resonator 1 includes a rectangular-shaped piezoelectric body 2, and electrodes 3a and 3b disposed on two opposite side surfaces of the piezoelectric body 2. The piezoelectric body 2 disposed between the two electrodes 3a and 3b is polarized in a direction that is perpendicular to the major surfaces of the electrodes 3a and 3b as shown by an arrow in FIG. 34. In this piezoelectric resonator 1, longitudinal vibrations are generated when an excitation signal is applied between the two electrodes 3a and 3b.
An example of an electronic component incorporating this piezoelectric resonator 1 is shown in FIG. 35. This electronic component 4 includes a substrate 5 made of an insulating material. Lead electrodes 6a and 6b are disposed on the substrate 5. A supporting member 7 made of, for example, a conductive material, is located on one lead electrode 6a. The supporting member 7 is made of, for example, an epoxy-based conductive resin having a hardness of greater than 50 units defined in the JIS-A standards and having an elastic modulus of greater than 10 MPa. The piezoelectric resonator 1 is fixed to the upper surface of the supporting member 7. One electrode 3a is connected to the supporting member 7 and the other electrode 3b is connected to a pattern electrode 6b via a lead wire 8.
The electronic component 4 constructed in the above-described manner is used for example as a resonator, in which longitudinal vibration is generated in the piezoelectric resonator 1 when an excitation signal is applied between the electrodes 3a and 3b. The generation of longitudinal vibration in response to the applied signal makes it possible to use the electronic component device 1 as a resonator or a discriminator.
In the above-described structure in which the piezoelectric resonator is supported by the supporting member, the supporting member causes leakage of vibration from the piezoelectric resonator, and the leakage of vibration can generate an anomaly such as a ripple in the electronic characteristics of the component. Furthermore, the supporting member must have a precisely uniform and completely even surface so that the piezoelectric resonator can be accurately and evenly mounted thereon. If the supporting member has an uneven or angled surface, the piezoelectric resonator undesirably contacts the substrate thus interfering with the vibration of the resonator. To avoid such interference with the vibration of the resonator, it is required that the piezoelectric resonator should be mounted on the substrate in a firm and stable manner, for example, by bonding both ends of the piezoelectric resonator to the substrate via an adhesive such as resin. However, if the piezoelectric resonator is bonded to the supporting member, the adhesive for bonding and the supporting member act as a load to the vibration. This means that when the piezoelectric resonator is bonded to the supporting member, a change occurs in the resonator characteristics such as the mechanical quality factor Qm or the resonance frequency of the resonator. To compensate for the change in resonator characteristics caused by the adhesive and the supporting member, an adjustment to the resonator must be made after mounting the piezoelectric resonator on the substrate.
In the conventional mounting technique, as described above, the piezoelectric resonator has to be mounted so that it is supported in a completely even and stable fashion and the resonator characteristics have to be adjusted after the mounting step has been completed. Thus, the conventional mounting and assembly technique requires complicated processes and highly precise mounting accuracy and additional corrective steps after mounting.